A simple solution, however, remains out of reach.
The Tupelo Police Department's Traffic Division nabs an average of 140 speeders annually on South Thomas since the widening project, which ended in May 2007. That figure doesn't include speeders stopped by the department's Patrol Division, said Traffic Officer Alan Chavers.
Chavers doesn't have statistics prior to the widening, but he said speeding wasn't an issue on South Thomas back then.
That's because a majority of motorists travel at the speed with which they feel most comfortable, according to Edward Raymond, Mississippi Department of Transportation assistant state traffic engineer. Regardless of the posted limit, he said, motorists will drive slower on narrow roads with no shoulders than they will on wide roads with wide shoulders.
They intuitively know what is safe and reasonable and will adjust their speeds accordingly. This tenet is common knowledge among traffic engineers, who use it to determine appropriate speed limits, and is repeated by national sources like the Institute of Transportation Engineers and the National Motorists Association.
"There is a correlation between when you widen roads and make them straight ... it does tend to lead to faster driving," Raymond said. "It's a psychological thing."
In the nearly five years since the city widened South Thomas, the Tupelo Traffic Committee has entertained three separate requests to raise the street's speed limit. The first request came just one month after the widening project ended. The most recent came in March, at the behest of at least six residents who claimed 30 mph is too slow.
Each time, the committee voted unanimously against an increase. Minutes from those meetings cite member concerns that, if motorists currently drive 40 mph in a 30-mph zone, they'll go 50 mph in a 40-mph zone.
Spring Lake resident Clifford Brock said that's nonsense. Brock was among the most recent group to petition for a speed limit increase because he said the current limit is unreasonable. He argued higher speed limits won't invite wanton recklessness.
"You know when you're driving safely, and you know when you're driving too fast and it's dangerous," Brock said. "Most people aren't going to push it. They're going to drive what they naturally feel is the right speed. I'm a slow-poke driver, and look down and I'm going 35-40 (on South Thomas). It's the natural speed."
He further alleged the current limit courts potential disaster, saying faster motorists illegally use the middle turn lane to pass those going the posted limit. It's a sentiment shared by the Michigan State Police, whose website states that "posting speed limits lower or higher than what the majority of drivers are traveling produces ... increased crashes due to tailgating, improper passing and reckless driving."
The Tupelo Police Department doesn't have accident data for South Thomas. But Municipal Court Administrator Larry Montgomery, who lives at the intersection of South Thomas and Cla-Wood Drive, said accidents have decreased.
"We used to have accidents all the time, people going off the road into the ditches," Montgomery said. "It's not like that anymore."
Setting a safe speed
Most traffic engineers set speed limits according to three factors: The 85th percentile rule, road conditions and crash history.
The 85th percentile rule says the safest speed is the one used by 85 percent or less of drivers during free-flow traffic. In other words, if you clock 100 vehicles during normal traffic conditions and plot their speeds from lowest to highest on a graph, the speed traveled by vehicle No. 85 is your safest.
"However, in no case should the speed limit be set below the 67th percentile speed of free-flowing vehicles," according to the National Motorists Association.
On South Thomas, the 85th percentile during a day-long speed study by the Tupelo Police Department was 41 mph. The study didn't list a 67th percentile speed, but it did include a 50th percentile. It was 36 mph.
Other factors also weigh into equation. Road conditions - traffic volume, width, number of lanes, driveways, intersections, hills, curves, sidewalks - can prompt engineers to raise or lower the limit. Despite being relatively flat, wide and smooth, South Thomas intersects with 17 streets and 57 driveways, including those leading to churches and an elementary school.
And though it connects two major roads - West Main Street and Cliff Gookin Boulevard - South Thomas is located in a heavily residential district with joggers and cyclists and kids playing.
"If we raise it to 45, some people will look at it and think, 'I got away with going 45 in a 30 and so now I can go 55,'" said Chavers, who also sits on the Tupelo Traffic Committee. "And they wouldn't be able to react to an environment change - a car backing out of a driveway, a kid running out of a yard, a dog running out of a yard.
"In a residential neighborhood the environment constantly changes as you move forward. And that's why we set the speeds to where we are to help the driver be able to stop, slow down or be able to move around an object or an incident that's in front of them."
Raymond said he's unfamiliar with South Thomas, which isn't a state road and therefore not under MDOT jurisdiction. But he said MDOT typically runs new studies when they get multiple requests for a speed limit change.
It's not known when Tupelo conducted its last formal study of South Thomas. The Tupelo Traffic Committee never recommended one after the three requests. City Engineer John Crawley didn't return a call for comment.
The most recent speed study for South Thomas was conducted in 2009 - it's the one that found the 85th percentile speed was 11 miles over the current limit. But the study didn't exclusively measure free-flow traffic, as is recommended in a true engineering analysis.
"If this request was coming to me, I'd send a guy out and do a speed study, then look at physical features - are there lots of driveways, is there a school in the area?" Raymond said. "It may not be a totally unreasonable speed limit. Then again, they could be getting into a speed trap situation."